Brush seals are bundles of wires, fibers or strands that can be metal, organic or synthetic. The material is chosen according to the environmental and operational conditions of the brush seal, i.e. according to the type of fluids to be kept leaktight, the temperatures and pressures present on either side of the seal.
Referring to FIG. 1, a joint of this type is used to separate two volumes or two chambers A and B that surround a revolving shaft 1. Preferably, the bundle of wires 2 is positioned radially relative to revolving shaft 1 and the end 2E of the bundle of wires touches the outer surface of revolving shaft 1. The bundle of wires 2 is fitted into a fixed support 3 that constitutes the seal support. If we consider the direction of air that flows through the seal and that is indicated by arrow F, an upstream ring 5 is preferably used that is located upstream of bundle of wires 2 and that is positioned using a fastening ring 7, said fastening ring being fastened in seal support 3. A downstream ring 6 is also used, said ring being fastened downstream of bundle of wires 2 and positioned to bear against a rib 4 of seal support 3. It should be noted that the inner diameter of downstream ring 6 is smaller than that of upstream ring 5. In other words, the bundle of wires 2 is born over a greater distance by the downstream ring than by upstream ring 5. End 2E of bundle 2 has a certain degree of freedom, particularly on the upstream end i.e. of the upstream ring 5. The seal thus separates two zones in which different pressures may be present.
Referring to FIG. 2, French patent application 2 607 893 discloses a brush seal that comprises several bundles, and more particularly three bundles in the example shown. The three bundles of wires 12 are fastened perpendicularly to revolving shaft 1 in relation to which they are used to separate several zones, particularly upstream zone A and downstream zone B that are positioned on either side of the assembly of three bundles of wires 12. The bundles of wires 12 are held by upstream ring 15 and downstream ring 16 and are positioned relative to a seal support 13 using a rib 14 of said seal support.
The technical detail of all these types of brush seals are well known. On the other hand, it is not always easy to produce high quality brush seals.
Brush seals can also be positioned axially, for example in semi-static applications or to equip a slaved axial seal. In this event, it is impossible to implement the standard techniques used in the design of metal radial seals.